Lymphoid Pathology

Question 1

Where are T cells produced?

Answer 1

Thymus

Question 2

Where are B cells produced?

Answer 2

Species variation:
Bone marrow - primates, rodents
Ileal Peyer’s Patches - ruminants, pigs, horses
Bursa of Fabricius - birds

Question 3

What are secondary lymphoid tissues?

Answer 3

Lymph nodes
Spleen
MALT - tonsils, BALT, GALT

Question 4

Lymph circulation through the lymph node

Answer 4

Afferent LV > subscapular sinus > paratrabecular sinuses > medullary sinuses > subcortical sinuses > efferent LV

Question 5

In which area of lymph nodes are B cells located?

Answer 5

Follicular areas

Medullary cords

Question 6

In which area of lymph nodes are T cells located?

Answer 6

Parafollicular areas

Question 7

Etiologies for lymph node enlargement of “lymphadenomegaly”

Answer 7

Lymphadenitis: infectious, immune, toxic
Neoplasia: primary or metastatic
Lymphoid hyperplasia: antigen stimulation, viral

Question 8

3 viruses that can cause lymphoid hyperplasia

Answer 8

Malignant catarrhal fever
BLV
FIV

Question 9

Lymphoid hyperplasia can be ____ or ___

Answer 9

Paracortical or follicular

Question 10

Etiology for lymph node hypoplasia (general and specific)

Answer 10

Primary immunodeficiency: combined immunodeficiency (CID) in Arabian foals or X-linked CID in dogs (Bassets, JRTs, Welsh corgis)

Question 11

Etiologies for lymph node atrophy

Answer 11

Viruses that replicate in lymphs and induce apoptosis/necrosis: canine distemper virus and canine parvovirus
Glucocorticoids
Chemo drugs, ionizing radiation, malnutrition, cachexia

Question 12

Red pulp functions in spleen

Answer 12

Erythrocyte storage
Antigen removal
Hematopoiesis/erythropoiesis
Erythrocyte destruction

Question 13

White pulp function in spleen

Answer 13

Acquired immunity

• Periarteriolar lymphoid sheaths = T cells
• Follicles = B cells

Question 14

Etiologies for decreased spleen size (uncommon)

Answer 14

Immunodeficiency, senile atrophy, wasting/cachexia

Lymphoid necrosis alone isn’t enough to decrease size usually

Question 15

Etiologies for a uniform splenomegaly that has a bloody consistency on cut section

Answer 15

Congestion - terminal (euthanasia assoc)

Torsion

Question 16

Etiologies for a uniform splenomegaly that has a firm, non-bloody consistency on cut section

Answer 16

Bacteremia/septicemia
Granulomatous splenitis
Hemolytic anemia
Lymphoma (or other lymphoid neoplasm)
Extramedullary hematopoiesis
Amyloidosis, storage disease

Question 17

Etiologies for splenic nodules/masses that have a bloody consistency on cut section**

Answer 17

Hematoma
Hemangioma/hemangiosarcoma
Nodular hyperplasia with hyperemia
Splenic infarct
Incomplete splenic contraction (PM finding)

Question 18

Etiologies for splenic nodules/masses that have a firm, non-bloody consistency on cut section

Answer 18

Nodular hyperplasia
Granulomatous splenitis, splenic abscess
Lymphoma (or other lymphoid neoplasm)
Metastatic neoplasm

Question 19

Common sites for hemangiosarcoma in dogs

Answer 19

Spleen
Liver
Right atrum
Lung

Question 20

Thymus function

Answer 20

Primary lymphoid organ responsible for T cell development and maturation

Question 21

Thymus structure

Answer 21

Cortex: primitive and maturing lymphocytes
Medulla: thymic epithelial cells and Hassall’s corpuscles, myoid cells, interdigitating cells and dendritic cells, lymphocytes

Question 22

Diseases associated with a small thymus

Answer 22

Thymic hypoplasia (CID)
Maturation and aging (involution)
Thymitis
Thymic atrophy (lymphocyte apoptosis/necrosis)

Question 23

Etiologies for thymitis

Answer 23

Porcine circovirus 2
Epizootic bovine abortion
Salmonella poisoning in dogs

Question 24

Etiologies for thymic atrophy

Answer 24

Viral: FeLV, FIV, canine distemper or parvovirus, EHV-1, feline panleukopenia
Glucocorticoids
Nutritional deficiency: starvation, zinc, protein
Toxins: lead, mercury, polychlorinated biphenyls

Question 25

Diseases associated with a large thymic

Answer 25

Thymic hemorrhage (young dogs)* Lymphoma Thymoma (epithelial component is neoplastic)

Question 26

Define lymphoproliferative disease

Answer 26

All neoplasms arising from lymphocytes

Question 27

Define lymphoma

Answer 27

Malignant neoplasm of lymphocytes, infiltrates and destroys lymphoid tissue and other tissue

Question 28

Define leukemia

Answer 28

Neoplasm of lymphocytes or hematopoietic cells arising from the bone marrow; bone marrow = primary site; circulating neoplastic lymphocytes can be a complication of lymphoma "lymphoma with leukemia"

Question 29

What five ways can lymphoma be classified?

Answer 29

``` Anatomic Immunophenotypic Pattern Cytologic WHO ```

Question 30

Lymphoma in dogs

Answer 30

Most common 5-11 y/o Boxer and Scottish Terrier = higher incidence Gamma herpesvirus associated with some B-cell lymphomas

Question 31

Most common anatomic form of lymphoma in dogs (others listed in order)

Answer 31

``` Multicentric* Alimentary Thymic Cutaneous Other - solitary or specialized ```

Question 32

Lymphoma in cats

Answer 32

Most common neoplasm of cats* | Young cats affected by FeLV (>50% are >5 y/o)

Question 33

Most common anatomic form of lymphoma in cats (others listed in order)

Answer 33

Alimentary* (often FeLV d) Thymic (often FeLV+) Multicentric (often FeLV+) Solitary (kidneys often)

Question 34

Lymphoma in cattle

Answer 34

Relatively common, usually >2 yr | Most forms caused by BLV - persistent lymphocytosis in 30% infected

Question 35

Anatomic forms of lymphoma in cattle from most to least common

Answer 35

Multicentric*: commonly in right atrium, may present with signs of CHF Cutaneous Thymic: 6-30 m/o, not assoc with BLV Calf form: Holsteins = genetic predisposition, <6 m/o (generalized, BM, liver spleen) Alimentary (rare) Solitary (spinal canal)

Question 36

Most common anatomic form of lymphoma in horses

Answer 36

Multicentric